Monolayer transition metal dichalcogenides bear great potential for photodetection and light harvesting due to high absorption coefficients. However, these applications require dissociation of strongly bound photogenerated excitons. The dissociation can be achieved by vertically stacking different monolayers to realize band alignment that favors interlayer charge transfer. In such heterostructures, the reported recombination times vary strongly, and the charge separation and recombination mechanisms remain elusive. We use two color pump-probe microscopy to demonstrate that the charge separation in a MoSe2/WSe2 heterostructure is ultrafast (∼200 fs) and virtually temperature independent, whereas the recombination accelerates strongly with temperature. Ab initio quantum dynamics simulations rationalize the experiments, indicating that the charge separation is temperature-independent because it is barrierless, involves dense acceptor states, and is promoted by higher-frequency out-of-plane vibrations. The strong temperature dependence of the recombination, on the other hand, arises from a transient indirect-to-direct bandgap modulation by low-frequency shear and layer breathing motions.

Phonon-Mediated Interlayer Charge Separation and Recombination in a MoSe2/WSe2Heterostructure

Altmann P.;Gadermaier C.;Ghirardini L.;Trovatello C.;Finazzi M.;Duo' L.;Celebrano M.;Cerullo G.;Dal Conte S.
2021-01-01

Abstract

Monolayer transition metal dichalcogenides bear great potential for photodetection and light harvesting due to high absorption coefficients. However, these applications require dissociation of strongly bound photogenerated excitons. The dissociation can be achieved by vertically stacking different monolayers to realize band alignment that favors interlayer charge transfer. In such heterostructures, the reported recombination times vary strongly, and the charge separation and recombination mechanisms remain elusive. We use two color pump-probe microscopy to demonstrate that the charge separation in a MoSe2/WSe2 heterostructure is ultrafast (∼200 fs) and virtually temperature independent, whereas the recombination accelerates strongly with temperature. Ab initio quantum dynamics simulations rationalize the experiments, indicating that the charge separation is temperature-independent because it is barrierless, involves dense acceptor states, and is promoted by higher-frequency out-of-plane vibrations. The strong temperature dependence of the recombination, on the other hand, arises from a transient indirect-to-direct bandgap modulation by low-frequency shear and layer breathing motions.
2021
2D Heterostructure
charge transfer
femtosecond pump-probe spectroscopy
TDDFT
transition metal dichalcogenides
File in questo prodotto:
File Dimensione Formato  
Manuscript_HS_chargetransfer.pdf

accesso aperto

: Post-Print (DRAFT o Author’s Accepted Manuscript-AAM)
Dimensione 2.89 MB
Formato Adobe PDF
2.89 MB Adobe PDF Visualizza/Apri

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11311/1171458
Citazioni
  • ???jsp.display-item.citation.pmc??? 6
  • Scopus 40
  • ???jsp.display-item.citation.isi??? 37
social impact